Phase change materials (PCMs) may release or absorb, respectively, or store, respectively, heat by melting or solidifying, respectively, within a defined temperature range, and thus function as latent heat storage materials. This principle of heat storage may also be used, for example, in the wall insulation of buildings. Such latent heat storage materials are, e.g. in the form of micro-capsules, introduced into the wall plaster or into gypsum plaster-boards and liquefy during the day with high heat input. The heat absorbed is stored in the wall and keeps the interior cool. Following cooling during the evening hours and at night, the liquid storages solidify and release the crystallization heat to the environment. In that, the interior is warmed up.
As latent heat storage materials, predominantly paraffins and paraffin mixtures are used. Commercially available paraffin mixtures for PCM applications are, for example, Rubitherm® 27 and Rubitherm® 31. The main component of the above Rubitherm® mixtures is C18 paraffin with a content of only 59 or 39% by mass, respectively. These paraffin mixtures consist of even- and odd-numbered linear paraffins in the chain length range of C17 to C21 or C17 to approx. C30, respectively, however, have a portion of linear chains of 98.0 or 95.6% by mass, respectively.
Paraffins may also be produced by hydrogenation of commercially available alpha-olefins. These, however, only have linearities of approx. 90 to less than 95% by mass in the C16 to C18 range, and have the disadvantage that due to the branched side products, their melting enthalpy is clearly lower in comparison to that of highly linear paraffins.
It was found, that mixtures of even-numbered and odd-numbered paraffins, such with different chain lengths and/or higher branched portions have the disadvantage that these have wide or several different melting peaks, wherein, when these peaks are too far apart with regard to the temperature, normally only part of the possible melting enthalpy can actually be used.